From: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Subject: mm: adaptive hash table scaling
Allow hash tables to scale with memory but at slower pace, when HASH_ADAPT
is provided every time memory quadruples the sizes of hash tables will
only double instead of quadrupling as well. This algorithm starts working
only when memory size reaches a certain point, currently set to 64G.
This is example of dentry hash table size, before and after four various
memory configurations:
MEMORY SCALE HASH_SIZE
old new old new
8G 13 13 8M 8M
16G 13 13 16M 16M
32G 13 13 32M 32M
64G 13 13 64M 64M
128G 13 14 128M 64M
256G 13 14 256M 128M
512G 13 15 512M 128M
1024G 13 15 1024M 256M
2048G 13 16 2048M 256M
4096G 13 16 4096M 512M
8192G 13 17 8192M 512M
16384G 13 17 16384M 1024M
32768G 13 18 32768M 1024M
65536G 13 18 65536M 2048M
The effect of this change on runtime is undetectable as filesystem
growth is not proportional to machine memory size as is currently
assumed. The change effects only large memory machine. Additional
tuning might be needed, but that can be done by the clients of the
kmem_cache_create interface, not the generic cache allocator itself.
The adaptive hashing is disabled on 32 bit systems to avoid confusion of
whether base should be different for smaller systems, and to avoid
overflows.
[mhocko@xxxxxxxx: drop HASH_ADAPT]
Link: http://lkml.kernel.org/r/20170509094607.GG6481@xxxxxxxxxxxxxx
[pasha.tatashin@xxxxxxxxxx: UL -> ULL fix]
Link: http://lkml.kernel.org/r/1495300013-653283-2-git-send-email-pasha.tatashin@xxxxxxxxxx
[pasha.tatashin@xxxxxxxxxx: disable adaptive hash on 32 bit systems]
Link: http://lkml.kernel.org/r/1495469329-755807-2-git-send-email-pasha.tatashin@xxxxxxxxxx
Link: http://lkml.kernel.org/r/1488432825-92126-5-git-send-email-pasha.tatashin@xxxxxxxxxx
Signed-off-by: Pavel Tatashin <pasha.tatashin@xxxxxxxxxx>
Signed-off-by: Michal Hocko <mhocko@xxxxxxxx>
Acked-by: Michal Hocko <mhocko@xxxxxxxx>
Cc: David Miller <davem@xxxxxxxxxxxxx>
Cc: Al Viro <viro@xxxxxxxxxxxxxxxxxx>
Cc: Babu Moger <babu.moger@xxxxxxxxxx>
Signed-off-by: Andrew Morton <akpm@xxxxxxxxxxxxxxxxxxxx>
---
mm/page_alloc.c | 25 +++++++++++++++++++++++++
1 file changed, 25 insertions(+)
diff -puN mm/page_alloc.c~mm-adaptive-hash-table-scaling mm/page_alloc.c
--- a/mm/page_alloc.c~mm-adaptive-hash-table-scaling
+++ a/mm/page_alloc.c
@@ -7180,6 +7180,21 @@ static unsigned long __init arch_reserve
#endif
/*
+ * Adaptive scale is meant to reduce sizes of hash tables on large memory
+ * machines. As memory size is increased the scale is also increased but at
+ * slower pace. Starting from ADAPT_SCALE_BASE (64G), every time memory
+ * quadruples the scale is increased by one, which means the size of hash table
+ * only doubles, instead of quadrupling as well.
+ * Because 32-bit systems cannot have large physical memory, where this scaling
+ * makes sense, it is disabled on such platforms.
+ */
+#if __BITS_PER_LONG > 32
+#define ADAPT_SCALE_BASE (64ul << 30)
+#define ADAPT_SCALE_SHIFT 2
+#define ADAPT_SCALE_NPAGES (ADAPT_SCALE_BASE >> PAGE_SHIFT)
+#endif
+
+/*
* allocate a large system hash table from bootmem
* - it is assumed that the hash table must contain an exact power-of-2
* quantity of entries
@@ -7210,6 +7225,16 @@ void *__init alloc_large_system_hash(con
if (PAGE_SHIFT < 20)
numentries = round_up(numentries, (1<<20)/PAGE_SIZE);
+#if __BITS_PER_LONG > 32
+ if (!high_limit) {
+ unsigned long adapt;
+
+ for (adapt = ADAPT_SCALE_NPAGES; adapt < numentries;
+ adapt <<= ADAPT_SCALE_SHIFT)
+ scale++;
+ }
+#endif
+
/* limit to 1 bucket per 2^scale bytes of low memory */
if (scale > PAGE_SHIFT)
numentries >>= (scale - PAGE_SHIFT);
_
--
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